A novel carbon cycle turbulence index identifies environmental and ecological perturbations

Earth’s history has been characterised by complex interactions between life and the environment, which are often difficult to resolve. Here, we propose a new carbon cycle turbulence index (CTindex), based on the carbonate-carbon isotope (δ13Ccarb) record, to measure the extent of environmental perturbation over the last billion years. The CTindex trend is closely linked to Phanerozoic biotic extinction rates (ERs), as calculated from a palaeobiology database, supporting a strong environmental control on biotic ERs. We use the empirical CTindex—ER relationship to compare the extent of environmental perturbation due to greenhouse gas emissions with that during the Permian-Triassic (PTr) transition (∼252 Ma), representing the most severe mass extinction of the Phanerozoic. At the current peak of fossil fuel emissions, the CTindex indicates a moderate future environmental perturbation. However, if fossil fuel emissions increase into the next century, a pronounced CTindex peak greater than that which occurred during the PTr transition is indicated, which suggests the potential for a severe “sixth mass extinction” in the future.